Style
This is.a bit of a romantic simplification, but most communist movements are split btw utopian idealist types who want to build a perfect avant guard egalitarian world and the practical types who just want to hang a few capitalists and get the workers (as in their buddies) to power. In the USSR Stalin was the leader of the down to earth side, and that split was apparent in the Red Army, with Tukhachevsky and his fellow staff officers who planned an avant garde mechanised army being purged while pratical "my horse never breaks down" types prospered. Notice how the idealist avant gard painters were brushed off in favor of boringly reliable realistic painters, how the intellectual boldness of the early years was removed.
We could have the idealist side stronger and more active inside the party, and let them have a few followers inside the NKVD. the USSR would be split btw conservative communists, lined behind Stalin, and progressive communists, lined up behind Tukhachevsky. Stalin would plan a purge, but progressive insiders would warn their faction and the progressives would stage a coup. OTL the progressives (and this term does not mean they were any less communist) were isolated because the party was totally dominated by conservatives, and inside the Army they had no control over the "bases"
Plausible, maybe not, but a "progressive communist" USSR were Anna Akhmatova would be dining with Tukhachevsky at a state dinner before the premiere of Eisenstein's movie of Mikail Bulgakhov's "the master and margarita"while giant Tupolev airliners overflow the Kremlin makes for great reading